Plastic drainage tube



Sept. 28, 1965 J. K. w BAINES 3,208,478

PLASTIC DRAINAGE TUBE Filed March 27, 1963 l6 l3 l6 l2 16 "I316 INVENTORJOHN K. w. BMNES United States Patent Office v 3,208,478 PLASTICDRAINAGE TUBE John Kenneth Wadsworth Baines, GideaPark, England,assignor of two-thirds, jointly, to Alec Sabin Baines and Thomas BryanCreasy Davis, Essex, England Filed Mar. 27, .1963, Ser. No. 268,316Claims priority, application Great Britain, Mar. 30, 1962, 12,377/62 6Claims. (Cl. 138-162) This invention relates to the formation ofirrigation or drainage tube from resiliently flexible plastics stripmaterial formed along its longitudinal'edges with'tabs and recesseswhich can be interlockedto knit together the adjacent edges of thecurled strip or of two adjacent curled strips, the tabs being insertedinto the recesses in the inward direction with respect to the tube soformed so that they lie against the internal surface of the tube wall;The invention is particularly although not exclusively applicable to theformation in situ ofcontinuous lengths of underground irrigation ordrainage'tube by feeding a pair of the strips downwardly into anunderground tunnel being formed progressively by a mole plough, andpassing the strip material longitudinally through an appropriatelyconstructed former die towed in the tunnel behind the mole plough, bywhich die the two strips are curledand the edges of one strip areinterlocked with those of the other to form a tube positioned in thetunnel.

One such apparatus for forming underground irrigation or drainage tubeis described in the present applicants co-pending patent applicationSerial No. 268,271, filed March 27, 1963.

An object of the presentiinvention is to provide a new and improvedpattern of interlockable tabs and recesses on the edges of each strip.

According to the present invention, one longitudinal edge of each stripis formed with a row of spacedtabs protruding outwardly from the edge,each tab having a head elongated in the direction parallel-to the stripedge and joined to the strip edge by an integral neck defined byundercut recesses at each side of the base of the head, and is formedadjacent to its other edge with a row of correspondingly spacedelongated slots each of which extends parallel to the edge of the stripand is long enough at its inner edge to allow the head of a co-operatingtab to be passed through it, and in which the outer edge of each slotcarries a secondary tab which is joined integrally to the margin of thestrip at the outer edge of the slot and extends across the centralregion of the slot towards its inner edge from which the tab isseparate.

Thus When the head of a tab on one edge of a curled strip is insertedinwardly into the co-operating slot of an adjacent edge of the strip, orof a second curled strip, being passed through the wide inner side ofthe slot, the inserted tab bears against the secondary tab extendingacross the slot and deflects it inwardly. The resilience of thedeflected secondary tab causes it to bear against the inner surface ofthe head of the inserted tab and arches the latter so that its endportions beyond the neck will be curled slightly inwardly with respectto the tube being formed and will cross the edges of the slot, therebyensuring that an effective latch is produced between the inserted taband at least one end of the slot into which it is inserted, thuspositively preventing the withdrawal of the inserted tab.

In a preferred form of the invention, each end of each slot is ofstepped form affording a right-angled step between its Wide inner sideand its narrower outer side, the length of the outer side of the slotbetween the two steps being slightly greater than the width of the neckof a co-operating tab but less than that of the head of the tab. Thusthe neck of the inserted tab will pass between the steps and the head ofthe inserted tab will be drawn'back from the longer side of the slot tolodge behind the steps at the narrow side of the slot to form aways, butone specific embodiment of the invention which will now be described byway of example only, with reference to the accompanying drawings inwhich FIGURE 1 is a profile view of a short length of tabbed and-slottedstrip,

FIGURE 2 is a perspective view showing a tab of one curled stripentering a slot of the adjacent edge of a second curled strip, and 1FIGURE 3 is a perspective view similar to FIGURE 2 but showing thecompleted interlock between the tabsand slots.

The plastics strip illustrated in FIGURE 1 is made of the resilientpolyvinyl chloride calendered sheet material known by the registeredtrademark Vyback, the specification of the sheet material being asfollows:

Thickness-0.03 inch. Weight-0.22 pound per sq. foot.

The strip 10 is formed along one edge with a row of spaced integral tabs11 of generally hammer-headed form, which protrude outwardly a distanceof approximately 0.312 inch from the longitudinal edge 12 of the strip,the head13 of each tab 11 being 1 7 inches wide measured in thedirection of the length of the strip edge 12. Each tab 11 is undercut atits root at each end by a small parallel-sided notch 14 to form a neckportion 15 which is inch wide and joins the head 13 to the edge 12 ofthe strip. The head is thus formed with two protruding ears 16 at itsends. The pitch of the tabs 11 is 1 inches.

Along and adjacent to the other edge 17 of each strip 10, which is of 4inches nominal width, is formed a row of elongated closed slots 18spaced equally apart at a pitch equal to that of the tabs 11, the slots18 and tabs 11 being precisely in register with one another along thetwo sides of the strip 10.

Each slot 18 is generally parallel-sided and is 1% inches long at itsinner edge 19, but only inch long at its outer edge 20, and is formedwith a small right-angled step 21 at each end, each step 21 leaving anarrow notch 22 some ,4 inch wide between itself and the end of thelonger edge 19 of the strip. These two aligned notches 22 permit thehead 13 of one of the co-operating tabs 11 to be passed through a slot18 at its longer side, the tab head 13 being caused to arch slightly forthe purpose.

To effect this arching of the tab head 13 as it is inserted in one ofthe slots 18, a secondary tab 23 of rectangular form is joinedintegrally to the margin of the strip 10 at the short outer edge 20 ofeach slot 18 and extends across the slot 18 as far as its other edge 19,from which the tab 23 is separate. Each tab 23 is some inch long, and iscentrally disposed with respect to the length of the slot 18, leaving agap on either side of the tab 23 between it and the adjacent step 21.

As the head 13 of a hammer-headed tab 11 is inserted inwardly into oneof the slots 18 as shown in FIGURE 2, to efiect a connection between thetwo adjacent edges 12 and 16 of the two curled strips 10, the head 13deflects the secondary tab 23 which forces it towards the wider side ofthe slot 18, Le. towards the longer inner edge 19, and at the same timethe secondary tab 23, by virtue of its resilience, arches the head 13slightly to facilitate its passing through the slot 18. This arching ofthe head 13 curls back the two ears 16 of the head which protrudePatented Sept. 28, 1965 beyond its neck 15 at each end, so that theseears 16 will cross the ends of the slot 18 behind the stepped portions21. When the curled strip is released it will tend to expand radiallyunder its own resilience, thus drawing back the head 13 as shown inFIGURE 3 so that its neck 15 will be against the shorter edge of theslot with the two cars 16 of the head 13 positively engaged behind thesteps 21 at the slot ends, thereby producing a positively latchedinterconnection between the tab 11 and the slot 18.

The pattern of co-operating slots 18 and tabs 11 described hasconsiderable advantages over known forms of tab and slot joint whichrely on an interference fit between inclined edges of undercut flaredtabs and tapered slots, in that the degree of dimensional tolerancepermismissible in manufacture is greatly increased. Moreover theliability of a tube formed from such curled strip to become disconnectedat a seam if one connected edge is pulled longitudinally relatively tothe associated edge to which it is connected by the engagement of thetabs in the slots, is very greatly reduced.

Strip having the tab and slot pattern described is particularly suitablefor use in forming underground irrigation or drainage tube using theapparatus described in the aforesaid copending patent application No.268,271, filed March 27, 1963.

What I claim as my invention and desire to secure by Letters Patent is:

1. Resiliently flexible plastics strip material one longitudinal edge ofwhich is formed with a row of spaced tabs protruding outwardly from theedge, each tab having a head elongated in the direction parallel to thestrip edge and joined'to the strip edge by an integral neck defined byundercut recesses at each side of the base of the head, and is formedadjacent to its other edge with a row of correspondingly spacedelongated slots each of which extends parallel to the edge of the stripand is long enough at its inner edge to allow the head of a eo-operatingtab to be passed through it, each end of each slot being of stepped formaffording a right-angled step between its long inner side and itsshorter outer side, the length of the outer side of the slot between thetwo steps being slightly greater than the length of the neck of acooperating tab but less than that of the head of the tab, and in whichthe outer edge of each slot carries a secondary tab which is joinedintegrally to the margin of the strip at the outer edge of the slot andextends across the central region of the slot towards its inner edgefrom which the tab is separate, the length of said secondary tab beingless than the length of the slot at the shorter outer side of the slot.

2. Strip material as claimed in claim 1, in which each slot has aminimum transverse dimension approximately equal to the thickness of thestrip material.

3. Strip material as claimed in claim 1, in which the length of eachslot is greater than the corresponding length of the cooperating tabs.

4. Strip material as claimed in claim 1, in which the free end of thesecondary tap extends into close proximity with the inner edge of theslot.

5. A length of tube formed from a single length of the strip materialclaimed in claim 1, the strip material being curled into tube form andthe tabs on one edge being inserted in the inward direction into thetube through the co-operating slots on the other edge of the tube andinterlocked therewith, the tabs lying against the internal surface ofthe tubes so formed.

6. Tube formed of two lengths of the strip material claimed in claim 1,each strip being curled through approximately and the tabs on one edgeof one strip being inserted in the inward direction into the interior ofthe tube through the co-operating slots on the adjacent edge of theother strip and being interlocked therewith, the tabs lying against theinternal surface of the tubes so formed.

References Cited by the Examiner UNITED STATES PATENTS 225,013 3/80Knobeloch 229-39 901,702 10/08 Glasspoole 138-157 1,178,748 4/16Nicholson 229-21 1,651,044 11/27 Sladky et al. 138-166 1,996,997 4/35Inman 229-39 3,038,205 6/62 Plummer 138-166 XR LAVERNE D. GEIGER,Primary Examiner.

EDWARD V. BENHAM, Examiner.

1. RESILIENTLY FLEXIBLE PLASTICS STRIP MATERIAL ONE LONGITUDINAL EDGE OFWHICH IS FORMED WITH A ROW OF SPACED TABS PROTRUDING OUTWARDLY FROM THEEDGE, EACH TAB HAVING A HEAD ELONGATED IN THE DIRECTION PARALLEL TO THESTRIP EDGE AND JOINED TO THE STRIP EDGE BY AN INTEGRAL NECK DEFINED BYUNDERCUT RECESSES AT EACH SIDE OF THE BASE OF THE HEAD, AND IS FORMEDADJACENT TO ITS OTHEREDGE WITH A ROW OF CORRESPONDINGLY SPACED ELONGATEDSLOTS EACH OF WICH EXTENDS PARALLEL TO THE EDGE OF THE STRIP AND IS LONGENOUGH AT ITS INNER EDGE TO ALLOW THE HEAD OF A CO-OPERATING TAB TO BEPASSED THROUGH IT, EACH END OF EACH SLOT BEING OF STEPPED FORM AFFORDONGA RIGHT-ANGLED STEP BETWEEN ITS LONG INNER SIDE AND ITS SHORTER OUTERSIDE, THE LENGTH OF THE OUTER SIDE OF THE SLOT BETWEEN THE TWO STEPSBEING SLIGHTLY
 3. STRIP MATERIAL AS CLAIMED IN CLAIM 1, IN WHICH THELENGTH OF EACH SLOT IS GREATER THAN THE CORRESPONDING LENGTH OF THECOOPERATING TABS.